People in the UK will have to prove they are 18 before being allowed to access pornography websites from next year, the government is to announce.
Websites will be legally required to install age verification controls by April 2018 as part of a move to make the internet safer for children.
Users may be asked to provide credit card details, as gambling websites do.
Companies breaking the rules set out in the Digital Economy Act face being blocked by their internet provider.
Under the plans, firms supplying payment and other services to the pornography websites could be notified about any breach.
A regulatory body will be asked to oversee and enforce the new rules.
It is thought this could be the British Board of Film Classification (BBFC) which already sets age limits for films.
The BBFC used to rate the suitability of computer games for certain ages but Pan European Game Information (PEGI) now does this.
'Most robust protection'
Digital minister Matt Hancock will formally begin the process, which was the subject of a 2016 consultation during David Cameron's government, in a written statement to the Commons later.
Mr Hancock said: "All this means that while we can enjoy the freedom of the web, the UK will have the most robust internet child protection measures of any country in the world."
Will Gardner from internet safety charity Childnet said: "Steps like this to help restrict access, alongside the provision of free parental controls and education, are key."
An NSPCC report in 2016 said online pornography could damage a child's development and decision-making and had been seen by 65% of 15-16 year olds and 48% of 11-16 year olds.
The study found 28% of children may have stumbled across pornography while browsing, while 19% had searched for it deliberately.